e force is perhaps the same."[1270] This idea
was confirmed on fuller investigation. In 1882 the appendages of
thirty-six well-observed comets had been reconstructed theoretically,
without a single exception being met with to the rule of the three
types. A further study of forty comets led, in 1885, only to a
modification of the numerical results previously arrived at.

In the first of these, the repellent energy of the sun is fourteen times
stronger than his attractive energy;[1271] the particles forming the
enormously long straight rays projected outward from this kind of comet
leave the nucleus with a mean velocity of just seven kilometres per
second, which, becoming constantly accelerated, carries them in a few
days to the limit of visibility. The great comets of 1811, 1843, and
1861, that of 1744 (so far as its principal tail was concerned), and
Halley's comet at its various apparitions, belonged to this class. Less
narrow limits were assigned to the values of the repulsive force
employed to produce the second type. For the axis of the tail, it
exceeds by one-tenth (= 1.1) the power of solar gravity; for the
anterior edge, it is more than twice (2.2), for the posterior only half
as strong. The corresponding initial velocity (for the axis) is 1,500
metres a second, and the resulting appendage a scimitar-like or plumy
tail, such as Donati's and Coggia's comets furnished splendid examples
of. Tails of the third type are constructed with forces of repulsion
from the sun ranging from one-tenth to three-tenths that of his gravity,
producing an accelerated movement of attenuated matter from the nucleus,
beginning at the leisurely rate of 300 to 600 metres a second. They are
short, strongly bent, brush-like emanations, and in bright comets seem
to be only found in combination with tails of the higher classes.
Multiple tails, indeed--that is, tails of different types emitted
simultaneously by one comet--are perceived, as experience advances and
observation becomes closer, to be rather the rule than the
exception.[1272]

Now what is the meaning of these three types? Is any translation of them
into physical fact possible? To this question Bredikhine supplied, in
1879, a plausible answer.[1273] It was already a current surmise that
multiple tails are composed of different kinds of matter, differently
acted on by the sun. Both Olbers and Bessel had suggested this
explanation of the straight and curved emanations from the comet